This invention relates to instruments for testing engine performance and more particularly to devices for measuring and indicating the power output of engines.
Prior copending application Ser. No. 135,300 of Albert B. Niles et al, filed Apr. 19, 1971 and entitled METHOD AND APPARATUS FOR CHECKING ENGINE PERFORMANCE, discloses a system for rapidly and accurately measuring the power output of an engine without necessarily removing the engine from a vehicle or other working context. Prior to the system of the above-identified copending application, highly accurate power measurements required removal of an engine from a vehicle or the like in order that it might be mounted in a complex engine stand dynamometer. Other available instruments, such as a chassis dynamometer, did not require removal of the engine from the vehicle but were inherently less accurate. A chassis dynamometer is coupled to the vehicle wheels and thus does not measure power output at the engine itself but instead measures power as diluted in a variable and unknown manner in the engine transmission and other drive line components.
Virtually all specific engine models have a known Specific Fuel Consumption factor which is defined as the weight of standard fuel consumed per unit power output per unit of time. If expressed in terms of pounds of fuel per brake horsepower per hour this factor is known as the Brake Specific Fuel Consumption. Although this factor varies somewhat at different engine speeds in a given model of engine, manufacturers customarily publish tables or graphs showing the Brake Specific Fuel Consumption factor at different speeds for each engine model. Basically, the power measurement system of copening applicaton Ser. No. 135,300 operates by measuring the rate of fuel consumption of the engine under test at a predetermined speed and at constant loading and then multiplies this rate by the known Brake Specific Fuel Consumption factor for that engine at the predetermined speed and by units and fuel density correction factors if necessary. The result is the brake horsepower output of the engine.
In order for the test to be accurate, the engine must first be checked to assure that various malfunctions such as improper timing or compression, localized or generalized overheating and the like are absent. In the absence of these readily detectable malfunctions, it may be reliably assumed that any deviation of the power output of the engine from the standardized known power output of such engines as manufactured must be traceable to a variation of the rate of fuel flow into the engine. In other words, any specific model of engine in proper working order converts a known percentage of the latent energy of incoming fuel into kinetic energy at the engine output. Accordingly, once it has been determined that the engine is in proper working order in conformance with the manufacturer's specifications, power output can be reliably computed from fuel input.
In order to simplify and facilitate engine power measurements by this technique, prior copening application Ser. No. 135,300 discloses a compact portable computer-like instrument which may be temporarily coupled to an engine to be tested by installing a digitizing flowmeter in the engine fuel lines and by attaching a digitizing tachometer to a rotary component of the engine. The Brake Specific Fuel Consumption factor for the engine model may be dialed into the instrument and the test may be started by operating a switch. The instrument then clocks the time required to consume a predetermined quantity of fuel in the engine and displays this time at a read-out window. The operator then manipulates another switch and the instrument performs the necessary computations as discussed above and ultimately displays the calculated horsepower output of the engine at the read-out window. Prior U.S. Pat. No. 3,722,265 also discloses a basically similar power measurement instrument.